1. Field of the Invention
The present invention relates to a method and apparatus for direct or indirect one-sided or double-sided application of a liquid or pasty coating medium onto a spliced traveling material web, notably of paper or cardboard.
2. Description of the Related Art
Methods and apparatuses for direct or indirect one-sided or double-sided application of a liquid or pasty coating medium onto a spliced traveling material web are employed in the framework of so-called coaters in order to provide a material web on one or both sides with one or several layers of a coating medium, for example, color, starch, impregnating solution or the like. Such a web travels at a high speed of up to about 2000 m/min, is formed for instance of paper, cardboard or a textile material, and has a web width up to about 8 meters.
In the so-called direct application, the normally pressurized liquid or pasty coating medium is applied directly onto the surface of a traveling material web by an applicator system or applicator mechanism. During application, the web is supported by a revolving countersurface, for example, an endless belt or a backing roll. In the indirect application of the medium, in contrast, the liquid or pasty coating medium is first applied onto a substrate surface, e.g., the surface of a roll configured as an applicator roll. The coating medium transfers from the applicator roll to the material web in a nip through which the material web passes.
Since a coating system, once set up, usually runs nonstop for both economical and technical reasons, it is necessary to join an expiring material web being coated, which in the uninterrupted operation of the system can be presented only in limited length on rolls or the like, to the material web of a new and unexpired material web roll. Thus is created, so to speak, a material web of "endless length." This joining of two material webs is carried out with the aid of generally known splicing methods and splicing apparatuses. It has been demonstrated, though, that web splices of a traveling material web frequently snap, notably when passing the coating system or applicator, leading to an undesirable interruption of the operation. Such snaps are an appreciable impairment to the productivity and profitability of the coating system. Consequently, minimizing the number of web breaks in splice passes is desirable.
Known from German Patent Document No. DE 195 00 402 A1 is an apparatus for showering a web passing by a showering point with a shower solution, using the so-called curtain principle. According to the principle, the shower solution is poured between two lateral shower holders onto the web, which is carried around a shower roll. The shower solution is poured solely by gravity as a free-falling curtain of solution having several layers. The web travels at a relatively low speed of about 300 meters/min and has a width in German Patent Document No. DE 195 00 402 A1 of about 1400 mm. The apparatus includes devices with which the shower curtain can be blocked when needed, so that it no longer impinges on the passing web. Employed as such a device is a so-called "start-stop plate," which suspends the showering by advancing into the shower curtain such that the solution is collected completely by the start-stop plate and passed into a container. To resume showering, the start-stop plate is retracted from the shower curtain and the solution again impinges onto the web passing the showering point. The apparatus taught in German Patent Document No. DE 195 00 402 A1 and the pertaining showering method according to the principle are usually employed in the manufacture of negative films.